Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$248.99	3.778%	$258.3968	$258.40	$258.40	$258.40
Purchase #2	$223.69	10.595%	$247.39	$247.39	$247.40	$247.40
Purchase #3	$126.29	13.163%	$142.9136	$142.91	$142.90	$142.90
Purchase #4	$89.72	10.414%	$99.0634	$99.06	$99.05	$99.10
Purchase #5	$132.97	11.428%	$148.1658	$148.17	$148.15	$148.20
Purchase #6	$199.96	7.812%	$215.5809	$215.58	$215.60	$215.60
Purchase #7	$112.81	10.464%	$124.6144	$124.61	$124.60	$124.60
7 purchase totals =	$1,134.43		$1,236.1249	$1,236.12	$1,236.10	$1,236.20